The invention relates to novel tin polyoxaalkanecarboxylates and to anti-tumour compositions containing such compounds.
The anti-tumour activity of tin compounds is known; it is also known that the anti-tumour activity of tin compounds could be enhanced by increasing their solubility in water.
The invention now provides water-soluble tin compounds which show strong in vitro anti-tumour activities against a broad spectrum of tumours, as appears from the experimental part, disclosed hereinafter.
More specifically the invention relates to tin polyoxaalkanecarboxylates having the formula
[(R1pR2qSn)rOs]t
wherein
R1 represents C1-C6 alkyl, branched or straight, substituted or not by one or more hydroxyl groups or halogen atoms, or a phenyl group, substituted or not by one or more hydroxyl groups or halogen atoms,
R2 is a carboxylic residue selected from: 
and p, q, r, s and t have the following meanings:
p=3, q=1, r=1, s=0 and t=1;
p=2, q=2, r=1, s=0 and t=1;
p=2, q=1, r=2, s=1 and t=2.
According to a preferred embodiment of the invention, represents R1 a phenyl group or a n-butyl group in a compound having formula (1), (2) or (3).
The compounds according to the invention can be synthesized by effecting a condensation reaction between a carboxylic acid having formula 
with triaryltin hydroxide, trialkyltin acetate or dialkyltin oxide, preferably triphenyltin hydroxide, tri-n-butyltin acetate or di-n-butyltin oxide, according to the following reaction schemes:
a) RCOOH+(C6H5)3SnOHxe2x86x92(C6H5)3SnOCOR+H2O
b) RCOOH+Bu3SnOCOCH3xe2x86x92Bu2SnOCOR+CH3COOH
c) 2RCOOH+Bu2SnOxe2x86x92Bu2Sn(OCOR)2+H2O
d) 2RCOOH+2Bu2SnOxe2x86x92xc2xd{[Bu2(RCOO)Sn]2O}2+H2O
Different media and methods can be used to synthesize such derivatives
1) the condensation can be performed in toluene/ethanol. The water formed during the condensation is eliminated by azeotropic distillation (Dean-Stark funnel)
2) benzene can be used instead of toluene/ethanol
3) these compounds can also be prepared by a two-step procedure, dibutyltin oxide being first condensed with n-propanol to yield tetrabutyldipropoxydistannoxane:
2Bu2SnO+2PrOHxe2x86x92(PrOSnBu2)2O+H2O
In a second step, the carboxylic acid is added at room temperature to this tetrabutyldipropoxydistannoxane in the desired molar ratio.
The compounds synthesized by one of these methods were characterized by elemental analysis, 1H, 13C and 117Sn NMR, electrospray mass spectrometry and 119mSn Mxc3x6ssbauer spectroscopy. Chromatography on Sephadex LH-20 proved to be a very efficient method to separate 3 (or 7) from 4 (or 8), or 11, 12, 15 and 16 from the starting carboxylic acid.
The structures of the compounds synthesized are depicted below 